<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>demo01</title>
</head>
<style>
    .container{
        height: 1200px;
        width: 100%;
        background-color: #0f0; 
     }
</style>
<body>
    <h1>demo01</h1>
    <div class="container"></div>
    <h3>bottom</h3>
</body>
</html>